028 stihl missing when tilted to left

[Brushwacker]

This is a problem I am not familiar with. Of course I have a couple ideas, but mabe somebody can save me some time that is familar with the symptoms.
A neighbor gave me this saw. He said it never run right since it was new,and he hasn't used it much,that was about it.
I poured the old gas out and the tank looked clean so I checked the spark plug and it was a cj8y gapped at .030 which I thinks to hot, so I put a new Bosch wsr6 gapped at .020. (The old plug had good color) It fired up in 3or4 pulls and was a bit sluggish reving so I checked the carb adj. both h & l were about 3/4 out so I set them to 1 and it sounded near perfect.
I had a storm blow down about a dozen medium and big trees this spring so I tackled a big white oak trunk that broke off a double. I cut about 4 tanks without a problem and was getting into about 16inch blocks. I had cut the top down and where it broke off was about 8 feet up so the log was about 50 to 60 degrees and I had the saw tilted accordingly flywheel side toward ground and just getting heavy in the cut, wide open and it started missing as if the plug was fouling and kept getting worse. I first noticed it I thought it was doing it when I was pushing it hard in the cut,but I believe it got worse cause of the angle. Thought mabe it was due to low fuel so I fueled up and it did the same thing. I turned the saw upside down and cut with the back of the bar a ways and it run fine,turned it backover and it started missing again. Is it a seal ? If so which one ? Or mabe it is shorting out some where at that angle ? Or is there another likely cause?
Did a search without success. If some can help I would appreciate it.
Thanks.

 

[Mad Professor]

Guessing, but fuel pickup line or a bad insulation on an ignition wire. Check that something is not shorting out ignition switch too.

I'd think if it was coil going bad would be hot enough before 4 tankfuls and not matter on angle of saw. If you get 4 good tankfuls I 'd think not vacuum leak or diaphram in carb either.

That being said, you might check the diaphram in carb, I pulled apart one full of sawdust. Not enough to stop it running but eough to cause a problem.

 

[sugarbush]

also should be pressure/vac tested and pull muffler to check piston/cyl. likely cause is leak in pulse line or carb to cyl boot.

 

[Kneejerk Bombas]

also should be pressure/vac tested and pull muffler to check piston/cyl. likely cause is leak in pulse line or carb to cyl boot.

+1

 

[Lakeside53]

Seals tend to leave you with no power and/or a weak throttle; ignition is a dead cut...

I'd inspect the ignition wire for wear/shorts, then do a full pressure/vac test to eliminate (or qualify) seal issues.

 

[Brushwacker]

I worked on it a little while last night and found the small black wire from the coil to the switch frayed and splitting, so I cut the bad out and put in a wire splice to reconnect it. Looked like when the saw tilted the weight shifted it enough to ground where the lighter colored kill switch wire connected to the top cover screw for a ground. We' ll see if that fixed it.
Thankyou much for all your replies.